1. Field of the Invention
The present invention relates to a substrate bonding apparatus for a liquid crystal display (LCD) panel, and more particularly, to a substrate bonding apparatus for an LCD panel that subdivides venting holes, thereby achieving an enhancement in uniformity of venting.
2. Discussion of the Related Art
As the information age advances, the demand for various display devices has increased. To meet this demand, research regarding flat panel display devices is ongoing including liquid crystal display devices (LCD), plasma display panels (PDP), electro-luminescent displays (ELD), vacuum fluorescent displays (VFD), and the like. Some flat panel display devices are being applied to various appliances for display purposes.
In particular, the LCD has been used as a substitute for the cathode ray tube (CRT) in association with mobile image display devices because the LCD has the advantages of superior picture quality, lightness, thinness, and low power consumption. Thus, the LCD is currently most widely used. Various applications for LCDs are being developed in addition to mobile image display devices such as monitors of notebook computers, but also TV monitors to receive and display broadcast signals and desktop computer monitors.
Although the LCD has been developed so that it can be used as picture display devices in various fields, the task to enhance the quality of images in such LCDs is made difficult by attempting to improve the above-mentioned features and advantages.
Accordingly, successful application of such LCDs to diverse image display devices depends on whether or not the LCD can realize desired high picture quality including high resolution, high brightness, large display area, and the like, while maintaining the desired characteristics of lightness, thinness, and low power consumption.
Methods for manufacturing the above-mentioned LCD are typically classified into a liquid crystal injection type and a liquid crystal dispensing type. In the liquid crystal injection method, a sealant pattern is written on one of upper and lower substrate such that the sealant pattern has an injection port. Thereafter, the substrates are bonded to each other under a vacuum condition. A liquid crystal material is then injected into a space defined between the substrates through the injection port. In the liquid crystal dispensing method, one substrate is prepared on which a liquid crystal material has been dispensed. Another substrate is prepared on which a sealant pattern is formed such that the sealant pattern extends completely along the peripheral edge of the substrate without forming an injection port. Thereafter, the latter substrate is arranged on the former substrate under a vacuum condition such that they are aligned with each other. The aligned substrates are then bonded to each other. Such a liquid crystal dispensing method is disclosed in Japanese Patent Application Nos. Heisei 11-089612 and Heisei 11-172903.
The liquid crystal dispensing method has an advantage in that the liquid crystal dispensing method uses a reduced number of processes by eliminating certain processes required in the liquid crystal injection method. For example, such processes may include forming a liquid crystal injection port, injecting a liquid crystal material, and sealing an injection port, and thus, does not use equipment for those processes.
For this reason, active research has recently been undertaken to provide various equipment for use in the liquid crystal dispensing method.
For example, the applicant proposed a substrate bonding apparatus for an LCD panel through Korean Patent Application No. 2002-71366 (Filing date: Nov. 16, 2002).
Where it is desired to bond an upper substrate (or a lower substrate) to a lower substrate (or an upper substrate) coated with a sealant along the peripheral edge of the lower substrate and with a liquid crystal material dispensed thereon, using the substrate bonding apparatus proposed by the applicant. The upper substrate is first attached to an upper electrostatic chuck (ESC) and is then lowered such that the upper substrate is near the lower substrate. The upper ESC is then turned off, thereby releasing the upper substrate which is, in turn, laid on the lower substrate. In this state, the substrate bonding apparatus performs a venting process to bond the upper and lower substrates to each other.
An example of the venting process is illustrated in FIG. 1A. As shown in FIG. 1A, during the venting process, a vacuum is formed in a space defined between an upper substrate 110 and a lower substrate 120, and sealed by a sealant 111 formed on the lower substrate 120, thereby generating a pressure difference between the space and the atmosphere. By virtue of the pressure difference, the upper substrate 110 and lower substrate 120 are bonded to each other.
However, as shown in FIG. 1B, the above-mentioned conventional substrate bonding apparatus has a problem in that venting is non-uniformly carried out in the venting process, thereby causing the bonding quality of the substrates to be poor. That is, when venting is non-uniformly carried out in the venting process, a gap is formed between the upper substrate 110 and the sealant 111. In this case, an air bubble may be introduced into the liquid crystal space, thereby causing the bonding quality of the substrates to be poor.